To realize a power amplifier using a MISFET formed on a silicon semiconductor, it is indispensable to stably flow a large current. Hence, a layout is widely used which arranges gates in a comb shape, which is a repetitive pattern of source electrodes, gate electrodes and drain electrodes and which shares the source electrodes and the drain electrodes between adjacent gates. This layout is generally referred to as a “multi-finger structure”.
The multi-finger structure causes a negative resistance component of an output from the drain electrode, and has a problem of an unstable RF operation due to this negative resistance component.